Aluminum alloy and anodes formed thereof



United States Patent 3,455,808 ALUMINUM ALLOY AND ANODES FORMED THEREOFBernard Raclot, Paris, France, assignor to Societe Generale duMagnesium, Paris, France No Drawing. Filed Mar. 17, 1966, Ser. No.535,030 Claims priority, application France, Oct. 1, 1965, 33,463 Int.Cl. C23f 13/00 US. Cl. 204-197 6 Claims ABSTRACT OF THE DISCLOSURE Agalvanic anode for cathodic protection of tanks formed of a non-sparkingaluminum alloy characterized by high constant potential and highelectrochemical efficiency consisting of .1 to 4 percent by weight zinc,0.2 to 0.6 percent by weight manganese, 0.005 to 0.1 percent by weighttitanium, 0.001 to 0.005 percent by weight beryllium, 0.05 to 0.15percent by weight mercury, with the balance being aluminum andimpurities.

This invention relates to an aluminum alloy containing mercury,titanium, manganese, beryllium and zinc as essential alloying elementsand to the method for preparation of same. It relates more particularlyto anodes, such as may be used for cathodic protection or for galvaniccells, formed of an alloy of the type described.

To the present, anodes having a practically constant potential andcharacterized by high electrochemical efficiency have been produced foruse in cathodic protection of alloys formed of aluminum and mercury.However, when aluminum is in contact with mercury or when formulatedwith mercury, the materials are subject to rapid oxidation in air. Itappears that mercury functions somewhat as a catalyst for the oxidationof aluminum whereby extremely small quantities of mercury are sufiicientto give the undesirable effects.

Stabilization against oxidation, without disturbing the electricalpotential or electrochemical efiiciency, can be effected by formulationof the aluminum-mercury alloy to include magnesium as an alloyingcomponent. However, such aluminum-mercury-magnesinm alloys are subjectto sparking responsive to engagement between the alloy and iron,particularly iron surfaces having a rust layer formed thereon. As aresult, such alloys present a danger when employed as an anode for thecathodic protection of tanks or containers housing combustiblematerials, such as petroleum products.

Anodes of magnesium or of aluminum-magnesium alloys are faced with theserious defect of spark generation when dropped or otherwise broughtinto frictional engagement with rusty iron surfaces. This is adisadvantage which has required the avoidance of such alloys andparticularly aluminum-mercury alloys containing magnesium in theconstruction of anodes for the protection of tanks containinginflammable materials such as petroleum products.

It is an object of this invention to produce and to provide a method forproducing an alloy based upon the presence of aluminum and mercury,which retains the desirable properties of relatively constant potentialand "ice Percent by wt.

Zinc 1-4 Manganese .2.6 Titanium .005. 1 Beryllium .001-.005 Mercury.O5.15

Balance aluminum, plus minor impurities of less than .2 percent.

In the preparation of the alloy, the alloying elements are preferablyintroduced into the molten aluminum as master alloys although othertechniques may be employed. For example, the titanium content can beintroduced by means of a master alloy of aluminum containing 4 percentby weight titanium. The manganese can be introduced as the master alloyof aluminum containing 10 percent by weight manganese, and the mercurycan be introduced with the zinc in a master alloy of zinc containing 15percent by weight mercury.

Mercury introduction is preferably performed by enclosing the mercurycontaining alloy in aluminum foil for submergence as a package into themolten bath of aluminum. This operates to free the mercury below thesurface of the bath thereby to avoid loss of mercury byvaporization.Thus fuller and safer utilization is made of the mercury introducedthereby to provide for better control of composition.

The following examples are given by way of illustration, but not by wayof limitation, of alloys embodying the practice of this invention andthe electrical characteristics of anodes formed thereof:

EXAMPLE 1 Percent Zinc 2.3 Manganese 0.48 Titanium 0.03 Beryllium 0.003

Mercury 0.125 Balance, 99.85% pure .aluminum.

In sea water, this alloy has the following characteristics:

Balance, 99.85% pure aluminum.

3 This alloy has the following potentials in sea water:

Volts Potential with an intensity of 50 ma./dm. 1.06 Potential with anintensity of 100 ma./dn1. 1.02 Potential with an intensity of 200ma./dm. 0.96

EXAMPLE 3 Percent Zinc 3.4

Manganese 0.58 Titanium 0.03

Beryllium 0.005 Mercury 0.10 Balance, 99.85% pure aluminum.

The potentials found in sea water are as follows:

Volts Potential with an intensity of 50 ma./dm. 1.04 Potential with anintensity of 100 ma./dm. 0.98 Potential with an intensity of 200 ma./dm.0.90

In the foregoing, the potential measurements are made with reference tosilver-silver chloride.

The electrochemical efficiency of the alloys exceeds 75% and :may urgeto as high as 85%, depending somewhat on the purity of the metals usedin the preparation of the alloy.

In the combination described, the zinc brings about a certain amount ofdepassivation of the aluminum but the amount of depassivation isinsuflicient, in the combination described, for eflicient cathodicprotection and the mercury component seems to overcome thisdisadvantage.

The manganese content operates in the combination described to stabilizethe alloy and prevent rapid oxidation, even when the mercury contentexceeds the amount necessary to obtain the desired potential. However,when the amount of manganese exceeds the upper limit described, theamount of passivation becomes excessive.

The beryllium operates in the combination to retard oxidation atelevated temperatures which might otherwise result in the formation of aresistant aluminum skin on the surface of the alloy.

When employed within the described range, the titanium operates in thecombination to provide improvements in the potential that is obtainedwith the alloy. When the titanium is employed in an amount in excess ofthat described, excessive passivation occurs.

While it is preferred to make use of an alloy containing zinc 'in theamounts described in combination with manganese, titanium and berylliumin the aluminum-mercury alloy, zinc is not essential. Thus an improvedalloy embodying the concepts of this invention may be formulated of thefollowing composition:

Percent by wt.

Zinc 4 Manganese .2-1.6 Titanium .005.1 Beryllium .00l.005 Mercury.05.15

Balance, aluminum plus impurities.

The alloy embodying the above modification may be represented by thefollowing example:

Balance, 99.036% pure aluminum.

Zinc .l4 Manganese .2.6 Titanium .005.1 Beryllium .00l.005 Mercury.05-.l5

Balance aluminum, plus minor impurities of less than .2

percent.

2. A galvanic anode formed of aluminum mercury alloy consistingessentially of:

Percent by wt.

Zinc .1-4 Manganese .2.6 Titanium .005.l Beryllium .001.005 Mercury .05.l 5

Balance aluminum, plus minor impurities of less than .2

percent.

3. A non-sparking aluminum alloy characterized by a relatively highconstant potential and high electro-chemical efiiciency consistingessentially of:

Percent by wt.

Zinc l-4- Manganese .2-l.6 Titanium .005-.l Beryllium .001.005 Mercury.05. l 5

Balance aluminum, plus minor impurities of less than .2

percent.

4. A non-sparking aluminum alloy characterized by a relatively constanthigh potential and high electrochemical efiiciency consistingessentially of:

Percent by wt.

Manganese .21.6 Titanium .005-.1 Beryllium .OO1.005 Mercury .05-.15Balance aluminum, plus tfl'lll'lOl impurities of less than .2

percent.

5. A galvanic anode for cathode protection of tanks containingcombustible materials consisting essentially of:

Percent by Wt.

Zinc l-4 Manganese .21.6 Titanium .005.1 Beryllium .001.005 Mercury .05.1 5

Balance aluminum, plus minor impurities of less than .2

percent.

6. galvanic anode for cathodic protection of tanks containingcombustible materials consisting essentially of:

Percent by Wt.

Manganese .21 .6 Titanium .005.1 Beryllium .00l.005 Mercury .05-.15

Balance aluminum, plus minor impurities of less than .2

percent.

(References on following page) .5 6 References Cited 3,318,692 5/ 1967Raclot 75138 UNITED STATES PATENTS 3,321,306 5/1967 Redmg et a1. 75146195 Rohrman 2O4 197 JOHN H g y y EX m1n r 5/1961 Fetzer et a]. 5 T.TUNG, Asslstant Exammer 11/1962 Snyder 75--138 US. Cl. X.R.

2/1963 Maeda 75138 75 13 14 2()4.. 143

